Digital dash

[Frederic Breitwieser]

A digital dash is not that difficult to do, both digitally controlled and
analog controlled.

For analog in, nat semi has a chip, the LM3914 which takes a 0-1V input and
spread it across 10 LEDs.  Two of these chips could make a 0-1V 20 LED scale
for more resolution, or a 0-2V scale if you perfer.  Most of the aftermarket
$100 oxygen sensor digital readouts are based on this premise. (Most o2
sensors produce 0-1V).  You can use op-amps to change the scale accordingly.

>From a digital perspective, its a matter of taking a certain number of bits
and making a readout in bargraph format.  I designed and started assembling
a dash for my mid-engine car, each graph having 16 rectangular LEDs.  16
LEDs translates into 4-bits... $0 to $F in hex.  So, the digital dash has a
single 8-bit input - the high order 4 bits (nybble) represent the gauge
address, and the lower 4-bits indicate the value.  Using simple 74LS154's
for the gauge display drivers for the bar graphs, and 74LS47's for the seven
segment displays, it was pretty easy to build.  Then, whatever I drive this
with, could be something as simple as a parallel port off a PC, any 8-bit
microprocessor, etc.

-----Original Message-----
From: Matt Cramer
To: diy_efi at diy-efi.org
Sent: 4/25/00 10:02 AM
Subject: Digital dash

	I've been thinking about building a digital dash for my Dart.
While I
could put together a circuit on my own that does LED bargraph readouts
without too much trouble, a three digit digital readout would be more
accurate.  Yesterday I decided to see if I could find any sites on the
Internet that might list what kind of IC's might be helpful in such a
circuit.  I got as far as figuring out that I could use some kind of off
the shelf 8-bit ADC, but is there some kind of chip that will take the
output from an ADC and use it to control a (preferably three digit) LED
display?  If so, what's it called, and who makes it?
	This would be enough for me to put together a digital
temperature gauge,
fuel gauge, or similar gauge, but I'm also wondering about tachometers
and
speedometers, as a digital tach would be a nice addition.  Is there some
kind of IC that will accept the kind of signal I can get from the
distributor as an input, and return a value that corresponds to its
frequency, or something else I could use for this?
	Thanks in advance.  There seems to be so many kinds of IC's out
there, I'm
not sure where to start!

Matt Cramer
'66 Dart, no EFI (yet)
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